System and method for navigation with limited satellite coverage area

ABSTRACT

A system and method for providing navigation through an underground space. The method includes receiving ephemeris data of a plurality of satellites in orbit at a location of the underground space, determining a schedule of the plurality of satellites in orbit, obtaining location of a plurality of pseudolites within the underground space, and determining satellite parameters to configure each of the plurality of pseudolites. Satellite parameters are determined based on the obtained location of each pseudolites and the determined satellite schedule. Also, the satellite parameters include at least a signal modulation parameter and a broadcast data parameter. The method also includes configuring each of the plurality of pseudolites with the respective satellite parameters, and controlling the plurality of pseudolites to broadcast satellite signals based on the determined satellite parameters. The broadcasted satellite signals simulate locations of the plurality of satellites in orbit.

TECHNICAL FIELD

The present disclosure relates generally to a system and method fornavigation, and more specifically, to a system and method for enablingnavigation of a vehicle in a limited satellite coverage area by managinga network of transmitters.

BACKGROUND

Satellites-based positioning systems are based on signals transmittedfrom satellites, or Space Vehicles (SV) (collectively referred tohereinafter as satellites or a satellite) orbiting earth that propagatethrough the atmospheric layers and reach an end user receiver. Thesignals received at a user side are used to measure the individual delayto each SV. Additionally, the SVs provide their ephemerides and clockinformation through periodically broadcasting messages that include theSVs' ephemeris and almanac data. Combining both the ranges measured withthe SVs' instantaneous position formulate a set of equations, wheretheir solution results in the users' position.

Also, Global Navigation Satellite System (GNSS) includes, as for today,four global operational constellations-Global Positioning Systems (GPS)(USA) with up to 32 satellites in orbit, Galileo (EU) with about 30satellites, Global Navigation Satellite System (GLONASS) (Russia) with24 satellites and Beidou (China) with 30 Medium Earth Orbit (MEO)satellites plus 5 Geostationary (GEO) satellites and about 16 more inthe Beidou2 system. Overall, while the number of orbiting satellitesexceeds 120, in practice some may be temporarily unavailable due to, forexample, maintenance reasons.

Further, GNSS receivers conduct range measurements by synchronizing thesignals code phase (i.e., base band version of the signal) and thecarrier phase (i.e., a radio frequency carrier phase) per visiblesatellite out of a superset of GNSS constellations, or the group ofsatellites within the GNSS that are working together. Some GNSSreceivers support most of the above-mentioned available constellationsconcurrently, such that range measurements are aggregated regardless ofspecific constellation. Here, the constellations are not geostationary,so managing the satellite's tracking and switching is performedconstantly at the receiver side. At any time, only part of the supersetof orbiting satellites is visible at any point on earth. With open skyconditions, approximately, ⅓ of the constellation is available forviewing at any time, which results in typical visibility of about 30SVs.

Position, Navigation and Time solution (PNT) typically requires at leastfour satellites in view with their corresponding measurements at a GNSSreceiver. In practice, more satellites are usually visible and are takeninto the calculation to reduce errors and improve robustness. Forexample, some GNSS receivers use filters such as elevation mask tofilter out low elevation satellites which usually induce larger errors.Other receivers scale as many satellites as possible with theirassociated received Signal-to-Noise-Ratio (SNR) to better optimize thePNT solution with the received noise. Multipath indicators and otherinformation may also be used to optimize PNT solution. In general,receivers combine as much existing information to best perform a PNTsolution given computation power or other limitations (e.g., battery,latency etc.). Finally, the PNT solution is vendor-specific, andconsidered to be a secret held by the equipment provider.

However, as the number of visible satellites falls, GNSS receivers maylose the ability to derive their PNT solution. Such cases may be foundin areas where sky visibility is limited, for example, in undergroundparking lots, in tunnels, under indoor scenarios such as at malls and inindoor stadiums, and so on. The general rule for these cases is wherethe sky visibility by the receiver antenna is very limited, and thenumber of concurrently tracked satellites drops below the minimalrequirements.

The related art suggests some solutions for incorporating beacontransmitters in GNSS indoor systems. In an example for such a solution,a GNSS beacon transmits a standard GNSS signal as if it is a satelliteorbiting in space, except that the beacon is not being maneuvered (i.e.,the beacon remains stationary), and the range is substantially shorterwhen compared to a GNSS standard satellite. As such, this solution islimited to indoor navigation applications.

Additionally, GNSS signal transmissions may be restricted due toregulatory limitations and spectrum frequency allocations that arereserved for military and civilian applications by regulators.

In view of the above discussion, there is a need for a solution thatwould allow accurate navigation when satellite's coverage is limited,while overcoming the deficiencies noted above.

SUMMARY

A summary of several example embodiments of the disclosure follows. Thissummary is provided for the convenience of the reader to provide a basicunderstanding of such embodiments and does not wholly define the breadthof the disclosure. This summary is not an extensive overview of allcontemplated embodiments, and is intended to neither identify key orcritical elements of all embodiments nor to delineate the scope of anyor all aspects. Its sole purpose is to present some concepts of one ormore embodiments in a simplified form as a prelude to the more detaileddescription that is presented later. For convenience, the term “someembodiments” or “certain embodiments” may be used herein to refer to asingle embodiment or multiple embodiments of the disclosure.

Certain embodiments disclosed herein include a method for providingnavigation through an underground space. The method includes receivingephemeris data of a plurality of satellites in orbit at a location ofthe underground space, determining a schedule of the plurality ofsatellites in orbit, obtaining location of a plurality of pseudoliteswithin the underground space, and determining satellite parameters toconfigure each of the plurality of pseudolites. Satellite parameters aredetermined based on the obtained location of each pseudolites and thedetermined satellite schedule. Also, the satellite parameters include atleast a signal modulation parameter and a broadcast data parameter. Themethod also includes configuring each of the plurality of pseudoliteswith the respective satellite parameters, and controlling the pluralityof pseudolites to broadcast satellite signals based on the determinedsatellite parameters. The broadcasted satellite signals simulatelocations of the plurality of satellites in orbit.

Certain embodiments disclosed herein also include a non-transitorycomputer readable medium having stored thereon causing a processingcircuitry to execute a process, the process includes receiving ephemerisdata of a plurality of satellites in orbit at a location of theunderground space, determining a schedule of the plurality of satellitesin orbit, obtaining location of a plurality of pseudolites within theunderground space, and determining satellite parameters to configureeach of the plurality of pseudolites. Satellite parameters aredetermined based on the obtained location of each pseudolites and thedetermined satellite schedule. Also, the satellite parameters include atleast a signal modulation parameter and a broadcast data parameter. Themethod also includes configuring each of the plurality of pseudoliteswith the respective satellite parameters, and controlling the pluralityof pseudolites to broadcast satellite signals based on the determinedsatellite parameters. The broadcasted satellite signals simulatelocations of the plurality of satellites in orbit.

Certain embodiments disclosed herein also include a system for mobileunderground navigation using a GNSS receiver. The system includes aplurality of a processing circuitry; and a memory, the memory containinginstructions that, when executed by the processing circuitry, configurethe system to receive ephemeris data of a plurality of satellites inorbit at a location of the underground space, determine a schedule ofthe plurality of satellites in orbit, obtain location of a plurality ofpseudolites within the underground space, and determine satelliteparameters to configure each of the plurality of pseudolites. Satelliteparameters are determined based on the obtained location of eachpseudolites and the determined satellite schedule. Also, the satelliteparameters include at least a signal modulation parameter and abroadcast data parameter. The system is also configured to configureeach of the plurality of pseudolites with the respective satelliteparameters, and control the plurality of pseudolites to broadcastsatellite signals based on the determined satellite parameters. Thebroadcasted satellite signals simulate locations of the plurality ofsatellites in orbit.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter disclosed herein is particularly pointed out anddistinctly claimed in the claims at the conclusion of the specification.The foregoing and other objects, features, and advantages of thedisclosed embodiments will be apparent from the following detaileddescription taken in conjunction with the accompanying drawings.

FIG. 1 is a diagram of a satellite network utilized to describe thedisclosed embodiment.

FIG. 2 is a block diagram of a GNSS system, according to an embodiment.

FIG. 3 is a diagram of an allocation of an orbiting satellite from alist of satellites available for allocation, according to an embodiment.

FIG. 4 is a diagram of a top-down view of a tunnel, according to anembodiment.

FIG. 5 is a flowchart illustrating a method for providing navigationunderground, according to an embodiment.

DETAILED DESCRIPTION

It is important to note that the embodiments disclosed herein are onlyexamples of the many advantageous uses of the innovative teachingsherein. In general, statements made in the specification of the presentapplication do not necessarily limit any of the various claimedembodiments. Moreover, some statements may apply to some inventivefeatures but not to others. In general, unless otherwise indicated,singular elements may be in plural and vice versa with no loss ofgenerality. In the drawings, like numerals refer to like parts throughseveral views.

The various disclosed embodiments include a method and system forsimulating Global Navigation Satellites System (GNSS) signals andtransmitting the same using pseudolites (pseudo-satellite) inunderground terrain. The system is deployed and operates concurrentlywith the existing GNSS satellites. Further, the disclosed system canoperate with standard GNSS receivers or modified receivers. In anexample embodiment, the system includes a plurality of transmittersdeployed inside the underground space. The transmitters may bepseudolites that are centrally controlled to transmit signals embeddingtheir positions. The simulated signals are compliant with the GNSSstandard signals, and the embedded positions simulate an existingreal-time GNSS constellation at the transmitters' (pseudolites)location. In an embodiment, a method for pseudolites self-locationderivation in the underground space is also provided.

FIG. 1 shows an example diagram of a satellite network 100 utilized todescribe the disclosed embodiment. The satellite network 100 includessatellites 110, 112, 114 in orbit. Also depicted in FIG. 1 is a vehicle120 approaching a tunnel 130 to illustrate a general case of amobile-connected device entering an underground space. Further, thevehicle 120 travels the tunnel 130 from its entrance 132 towards itsexit 134. The vehicle 120 is equipped with a GNSS receiver (not shown)to receive transmission signals from a Control and Management Server(CMS) 150, and a wireless connection (e.g., cellular, Wi-Fi, etc.)(notshown) for communicating with other components of the satellite network100. Along the tunnel walls there are transmission lines 136 and 138(indicated by dash dotted lines) are installed on the tunnel side walls,floor, ceiling, or a combination thereof.

According to disclosed embodiments, a plurality of pseudolites (ortransmitters) 140, 142, 144, 141, 143, and 145 are mounted along thetransmission line 136, 138, with an inter-pseudolite distance of severalmeters (e.g., 50-100 meters). It should be noted that the number ofpseudolites may be more than 6. In an example configuration, pseudolites140, 142, 144 are associated with one side of the wall (e.g., right-handwith respect to the vehicle 120 heading into the tunnel 130, generally),while pseudolites 141, 143, 145 are associated with the opposite sidewall, correspondingly.

All the pseudolites 140-145 are configurable and their radio signalparameters are controlled. Further, the configuration of such parametersmay be performed remotely. In an embodiment, the controllable parametersinclude timing, satellite modulation code, data, power, and so on. Thedata may include metadata, ephemeris and in general refers to the databroadcasted by the pseudolite.

In an embodiment, the configuration of each parameter can be loaded withtime stamp where at least one of the pseudolites 140-145 begins totransmit a compliant signal with the newly loaded configuration. Thatis, at least one of the pseudolites 140-145 is able to broadcast asignal (i.e. of previously loaded configuration) and concurrentlyreceive a new configuration, store the new configuration, prepare thenew signal, and switch to the new configuration signal upon indicationfrom the time-stamp indicates.

In an embodiment, the CMS 150 is adapted to monitor, configure, andcontrol the pseudolites 140-145. By configuring and controlling thepseudolites 140-145, the following parameters can be set: signal delaywith respect to the GNSS time coordinates, constellation selection(i.e., the selection of satellites 110-114 to work together within theGNSS) and satellite ID signal parameters (e.g. constellation: Galileo,Glonass, GPS or Baidou and SV id=[1,2,3, . . . ] etc.); broadcasted data(e.g. ephemeris data) of the satellites, 110-114, and so on.

In an embodiment, the CMS 150 may be implemented as a physical machine,a virtual machine, or combination thereof. An example block diagram ofthe CMS 150 is discussed below.

The CMS 150 may be deployed in a cloud computing platform, a datacenter, or on-premises (e.g., in a traffic control room). Also, the CMS150 may be centralized or distributed system. Further, the CMS 150 mayreceive or provide information over the network regarding the GNSSconstellation state among the satellites 110-114 and pseudolites 140-145surrounding and within the tunnel's area, including corrections andparameters to improve control and performance. Here, the GNSSconstellation refers to the satellites 110-114 and the pseudolites140-145 that work together within the GNSS.

The CMS 150 is configured to turn on and off some or all of thepseudolites 140-145, on demand. The CMS 150 may serve several tunnels,or may be allocated to a single tunnel or tunnel segment.

The CMS 150 is also connected to each of the pseudolites 140-145 via acommunication link 160 with all the pseudolites 140-145, where controlsignals may be transmitted from the CMS 150 to the pseudolites 140-145.Without loss of generality, the communication link 160 in FIG. 1illustrates a star configuration of the CME control network of thepseudolites 140-145. Other configurations are also considered withoutloss of functionality such as, ring, mesh, hybrid, and the like. Thecommunication link 160 may be wireline, such as dedicated wiring, orover powerlines or leased wirelines to name a few. Other configurationssuch as wireless connections, fiber, or combination of those are alsonoted as potential communication connections.

The satellite network 100 further includes a GNSS receiver 170 connectedthrough a data link 172 to the CMS 150. The GNSS receiver 170 isutilized to collect real time information of the GNSS scene in the areaof the tunnel 130, and to monitor signals received from the pseudolites140-145 to conform to regulations. The GNSS receiver 170 may also be inthe form of several receivers deployed in close vicinity to eachtunnels' exit. The data collected through data link 172 provides a realtime status of the GNSS constellation and visible satellites 110-114 outof the tunnel 130, along with the satellites' location (i.e., azimuthand elevation) and heading (i.e., whether satellites 110-114 are risingor setting).

It should be noted that a standard GNSS receiver 170 typically includesa radio circuit connect to an antenna, a measurement engine, and apositioning engine. The positioning engine converts a list of rangemeasurements (provided by the measurement engine) to satellites andtheir respective locations. The positioning engine may also determine aset of calibration parameters related to the receivers' location. Thepositioning engine is also responsible to turn range-rate measurements(also provided by the measurement engine) to receivers' velocity.Additionally, the positioning engine estimates the receiver clock biasand metrics indicating the quality of the resulting estimates (e.g.two-dimensional root mean squared error—2 dRMS, three-dimensional rootmean squared error—3 dRMS, Geometric dilution of precision GDOP etc.).The data provided by the engine may be utilized by an application (e.g.,a map app).

In an embodiment, the functionality of a position engine may beimplemented in the CMS 150. In another embodiment, discussed below, aposition engine included in a standard GNSS receiver (e.g., receiver170) may be utilized. In an yet another embodiment, a standard GNSSreceiver (e.g., receiver 170) is updated (e.g., through a softwareapplication or code) to support the functionality of a position engine.

According to the disclosed embodiments, the CMS 150 is configured tocontrol the pseudolites 140-145 to generate and transmit signalssimulating the satellites 110, 112, 114. That is, pseudolites 140-145radio signals to which to any GNSS receive in the vehicle would beviewed as legitimate satellites signals providing the accurate locationof the vehicle.

In an embodiment, each of the pseudolites 140-145 may be implemented asa software-defined radio circuit (not shown) to allow the CMS 150 tofully set the signals transmitter by a pseudolite. Software-definedradio is a radio communication system where components that have beentraditionally implemented in hardware (e.g. mixers, filters, amplifiers,modulators/demodulators, detectors, etc.) are instead implemented bymeans of software on embedded system. The operation of the CMS 150 isdiscussed in greater detail in FIG. 2.

FIG. 2 illustrates an example block diagram of a GNSS system 200,according to an embodiment. The GNSS system 200 includes a pseudolitespositions database 210, the CMS 150 connected to the 210 via aninterface 220, a pseudolites cluster 230 connected to CMS 150 viaanother interface 240, and the GNSS receiver 170 connected to the CMS150 via the interface 172.

The CMS 150 is configured to collect real time data (i.e., ephemerisdata of satellites 110-114 and pseudolites 140-145) from GNSS receiver170 through an interface, such as a data link 172. Here, the GNSSreceiver 170 may either be located in close proximity of or remotely tothe CMS 150. In both cases, the data may be transmitted to the CMS 150through the data link 172, which could be wireless or wireline orcombination of both under a proprietary or standard-based communicationprotocol. Also, data collected by the CMS 150 includes the locations ofsatellites 110-114 that have a clear Line-of-Sight (LOS) of the tunnel130, and the headings of the satellites 110-114. Further, by “realtime,” it is meant that the data that is transmitted to and collected bythe CMS 150 is substantially instantaneous, within a range from a fewseconds to a few minutes in lag time.

Separately, the data collected (e.g., by the CMS 150) regarding thepositions of the pseudolites 140-145 may be stored in the database 210.The database 210 may be connected to the CMS 150 through a network, ormay be coupled to the CMS 150-through an interface 220.

A cluster of pseudolites 230 also interfaces with the CMS 150, mountedalong, for example, the tunnel 130 (see for example, FIG. 1, above). Forthe sake of illustration, the pseudolites 140-145 are indexed by 1 to Nfor the right side wall and left (i.e., opposite) side wall,correspondingly using a subscript tuple (x,s), where x indicates thepseudolite index, and s indicates the side of wall. For “s”, “L” and “R”indicate the “left” and “right” sides of the wall in the tunnel 130,correspondingly. However, the numbering methods can be selected freelyas long as the pseudolite index is unique for the sake of system controland setting up. In an embodiment, the structure of the cluster ofpseudolites 230 is controlled through an interface 240.

In an embodiment, the CMS 150 includes an Input/Output (I/O) networkinterface 252, a processing circuit 254, such as a central processingunit (CPU), and a memory 256. Additionally, a processing circuit 254, ascheduler 262, a configuration manager 264, a pseudolites controller 266may separately be included in the CMS 150.

The scheduler 262 is configured to receive the satellites constellationdata from the data link 172, and generate a satellites schedule of thesatellites 110-114 (i.e., ephemeris data) for the pseudolites cluster230. In an embodiment, the satellites schedule may include the currentlynon-visible list of satellites 110-114 (i.e., satellites 110-114 thatmay not be visible to the GNSS receiver 170) complimentary to theschedule delivered by the GNSS receiver 170 through the data link 172regarding all of the available satellites 110-114 circling above thetunnel 130. The schedule prevents the signals transmitted fromsatellites 110-114 in view of the GNSS receiver 170 from colliding withthe pseudolites transmissions at any given time point, in order to avoidGNSS signal from being interfered by signals from the pseudolitescluster 230, and to avoid satellites/pseudolites metadata conflicts. Asthe constellation of the satellites 110-114 changes with time, thescheduler 262 is configured to refresh the list in order to comply withthe regulation and the baseline of interference-free system.

In an embodiment, an implementation of the scheduler 262 for managing alist of satellites 110-114 that are not in view of the GNSS receiver 170is presented below, as will be described in detail in FIG. 3. The listis ordered by the satellites' expected non-visible time period, where asatellite that is closer in time to become available for allocation, oris available for a longer time period is given a higher priority in thelist. This list can be managed by tracking the historical orbits of thesatellites, as the satellites cyclically orbit the Earth. Here, theupdate rate of the list in a periodical implementation (i.e. synchronousfashion) can be around once per few minutes, based on the satellite'sangular velocity. In an embodiment, the update of the list may betriggered by demand. At the same time, the pseudolites are allocated tothe list of satellites needs to be repeatedly refreshed by the scheduler262.

As an allocated satellite moves close to a position visible to the GNSSreceiver 170 (e.g., rising satellite), a change of a pseudoliteallocated with this satellite needs to be taken in order to avoidcollision of transmission signals sent from the pseudolites and therising operational satellite. Here, “satellite ID” is used for aspecific pseudolite allocation with the operational satellite, as an‘indexed satellite’ or ‘identified satellite’. A satellite ID allocationprocess implements a “pulling” of a highest priority satellite ID fromthe top of the satellite scheduling list, and a “plugging” of a separatepreviously released (i.e., pulled) satellite ID to the bottom of thelist for future use (i.e. the lowest priority in the list). An exemplaryoutlined disclosed implementation flow is presented in FIG. 3.

Once a satellite ID schedule changes, the scheduler 262 is configured tosend a message indicating a new schedule through interface 272 to aconfiguration manager 264. The message sent through the interface 272can be in many forms, including a full list of satellites andpseudolites within the new schedule, a differential list including onlythe pseudolites, or a single pseudolite schedule and its associatedsatellite ID allocation. The protocol of the message can be in the formof push or pull.

The configuration manager 264 is configured to derive a set ofparameters to configure the pseudolites 141-145 based on the pseudoliteposition (i.e. as noted in the pseudolite positions database 210 andaccessed through interface 220, and the satellite ID (provided from thescheduler 262 through interface 272). The pseudolites 141-145 may beconfigured to include a set of parameters that configure the pseudolitetransmission to be compliant with the GNSS system. Therefore, from theGNSS receiver's perspective, when the pseudolite transmission isreceived by the GNSS receiver 170, the transmission would appear as ifthe pseudolite was an authentic satellite in orbit. The parameters maybe classified into two segments: physical signal modulation parameters;and broadcasted data.

With respect to the physical signal modulation parameters, the examplesof the parameters may include the modulation pseudorandom code, andtiming alignment with respect to the GNSS system and transmission power.Also, with respect to the broadcasted data, the parameter may includethe satellites ephemerides parameters. These satellites ephemerisparameters are manipulated so that the derived satellite position andthe pseudolite position (i.e., the position) may be derived and storedin the pseudolites positions database 210).

As the ephemerides are derived from the broadcasted ephemeris data fromthe satellites 110-114, which includes over fifteen parameters,manipulation of the pseudolite location can be performed in many ways.An example of ephemeris data manipulation is to shift the timecoordinate of a pseudolite with respect to the GNSS standard time (i.e.using t_(oe), the time reference for the ephemeris data). Otherparameters manipulation may include locating the pseudolite in spaceright above the pseudolite location. Here, “right above” is a positionon a line connected towards the center of the Earth, the line includingthe pseudolite location and a point on the line at an altitude of 20,000km above a surface of the earth, the point in space being scaled backtoward the Earth surface at the GNSS receiver 170 side by a known factor(roughly ⅓). This method projects the computed location to Earth'sground level where the cluster of pseudolites 230 typically reside. Inan embodiment, a satellite clock bias may be manipulated to be fixed,and the broadcasted satellites orbit parameters may be set up, so thatthe pseudolite position reflected from a broadcasted satellite orbitparameter will end up in the pseudolite's exact location in the tunnel,which may be used to determine the pseudolites' position.

An additional way to manipulate the pseudolite location is by pluggingnon-conventional values into one or few parameters to signal the GNSSreceiver 170 that the interpretation of the ephemeris data needs to beother than standard. Here, some of the above listed approaches may notcomply with standard GNSS receiver ephemeris data decoding methods.However, the expected result of the later proposed approach may cause adenial of service to a conventional receiver, while enabling service toallowed customers.

In an embodiment, a field (e.g., SVhealth field) may be configured toindicate malfunctioned satellite, which may be ignored by regular GNSSreceivers 170, but may be used by receivers 170 that have been allowedto access. In an embodiment, an additional set of ephemerides may besent from the CMS 150 to allowed users. Here, general receivers 170,will ignore the pseudolites signals, but allowed receivers may acceptthe pseudolites' signals. Alternatively, an additional set ofephemerides over the network may be sent from the CMS 150 to allowed(e.g., registered) users. One example of this approach is bytransmitting a t_(oc) parameters with value larger than 38400 (which isout of the valid range for this parameter) to the allowed users.

Similarly, the metadata can be transferred to the allowed users via awireless communication interface, ensuring that only registered users tothe service can use the signals transmitted from the pseudolites allowsfor security of data transmission from the pseudolites. The transferringof the metadata via the wireless communication interface enables moreflexibility in formatting parameters in a non-standard manner (i.e., notcompliant with GNSS specifications). Furthermore, the cluster ofpseudolites 230 can each be assigned with identification numbers(satellite ID) of non-operative/non-existing satellites. Additionally,the system 200 may also leverage the status of healthy broadcastedfields as part of the pseudolites ephemeris, by setting the service in amanner so that regular receivers will omit the satellites 110-114, yetreceivers of registered users will be able to use the satellites110-114.

In another embodiment, the location of the pseudolites 140-145 inside atunnel 130 or an underground space may be transmitted to the GNSSreceiver 170 via an external communication link, such as the data link172 (towards which the receiver 170 is communicatively connected). Thiscan be performed, for example, in a peer-to-peer communication format,where each of the pseudolite 140-145 reports its location to thereceiver 170 in close vicinity over a short-range communication link(e.g. UHF, Wi-Fi, Bluetooth, etc.).

In an embodiment, a pseudolite location may be published in a list overa server (not shown) where the receiver 170 may retrieve thepseudolites' location. In another embodiment, the pseudolites' metadatamay be broadcasted by the first pseudolite in the tunnel 130 (i.e., thepseudolites 140 closest to the entrance 132 of the tunnel, representingall of the pseudolites within the entire tunnel structure to anapproaching mobile device within the approaching vehicle 120. It shouldbe appreciated that although this latter option may not comply with astandard GNSS receiver, decoding and processing flow enable provisioningcontrol to a closed group of customers base only.

Returning to FIG. 2, the GNSS receiver 170 includes an antenna 290, anantenna interface 292, a measurement engine 282, a positioning engine284, an interface 294 connecting an output of the measurement engine 282to the positioning engine 284, an application 286, and an interfaceconnecting the positioning engine 284 to the application 286.

The measurement engine 282 provides range and range-rate measurementsbased on signals received from the antenna 290 over the interface 292.The positioning engine 284 determines a list of range measurements fromthe GNSS receiver 170 to the satellites 110-114, and the respectivelocations of the satellites 110-114. In an embodiment, the positionengine 284 may also determine calibration parameters to the location ofthe GNSS receiver 170.

To derive the location of the satellites 110-114, the position engine284 within the GNSS receiver 170 implements the pseudo ranges withmultilateration algorithms. Here, the positioning engine 284 isconfigured to convert the range-rate measurements provided also by themeasurement engine 282 through the interface 294 into receivers'velocity. Additionally, the positioning engine estimates the receiverclock bias and metrices that indicate the quality of the resultingestimates (e.g. two-dimensional root mean squared error—2 dRMS,three-dimensional root mean squared error—3 dRMS, Geometric dilution ofprecision GDOP etc.).

The results determined by the positioning engine 284 are furthertransmitted through the interface 296 to an application 286 that usesthe location estimate of the satellites 110-114 for potentially:displaying the results, and controlling or communicating with otherelements of the GNSS system 200.

Further, the communication interfaces 294 and 296, and other similarinterfaces discussed transfer digital communication as is, or aftercompressing the data to be transferred. Correspondingly, the interfaces294, 296, along with the other interfaces discussed, may decompress thedata received for communication efficiency, power consumption reduction,and the like. The same may apply for wireless communication interfaceswhere data is transferred bidirectionally with remote entities.

In another embodiment, a mobile user receiver (not shown) can receivewith the pseudolites positions (obtained from the pseudolites positionsdatabase 210). Further, the pseudolites positions held in thepseudolites positions database 210 assist the GNSS receivers 170 bytransmitting the ephemeris of real GNSS of the satellites 110-114 thatare available at the tunnel exits 134 provided by the cloud or CMS 150.Conventional GNSS satellite signal acquisition performance may beenhanced once the vehicle 120 exits the tunnel 130. Therefore, thedisclosed embodiments provide a smooth transmission of signals when thevehicle 120 navigates into and out of the tunnel 130.

In FIG. 2, the configuration parameters as discussed previously aretransferred to a pseudolites controller 266 within the CMS 150 throughan interface 274. The pseudolites controller 266 is configured totranslate the configuration parameters, and is configured to set up aselected pseudolite, so that the selected pseudolite will comply withthe required signal generation protocol.

In an embodiment, the satellite parameters provided by the pseudolitescontroller 266 may generate a samples vector that is transmitted to theselected pseudolite, where the pseudolite up-converts the samples vectorto radio frequency (RF) and broadcast the samples vector. With the flowlisted here the entire baseband signal generation is carried outremotely out of a pseudolite system, and the pseudolite may upconvertthe baseband samples to radio frequency.

In another embodiment, the pseudolites controller 266 is configured tosend the satellite parameters as they are, or may compress or encode thesatellite parameters based on a pre-defined encoding scheme to thecluster of pseudolites 230. The control data set may define a time stampthat identifies the cluster of pseudolites 230 that will starttransmitting the new configuration signal. This later approach impliesthat each of the cluster 230 of pseudolite has an internal computing andprocessing entity that is able to generate the baseband signal samplesfrom the satellite parameters delivered and upconvert the basebandsignal samples to a compliant GNSS radio signal onboard.

The cluster of pseudolites 230 receives the control data and othersatellite parameters through an interface 240. Here, the space structureof the cluster of pseudolites 230 is represented by two columns. Eachpseudolite subscript tuple (i,j) indicates the pseudolite index alongthe tunnel 130 and the tunnel side where ‘L’ stands for ‘left side’ and‘R’ indicates the tunnels' ‘right side’. It is important to note thatthis simple indexing method given here is for illustration purpose only.Other naming and indexing methods are acceptable as long as the clusterof pseudolites 230 are uniquely identified by the pseudolite controller266. For example, any arbitrary single dimensional (1D) indexing (i),two dimensional (2D) indexing (i,j) or three dimensional (3D) indexing(i,j,k) where i, j and k are indexes suites this need. The 3D case maybe use, as an example, for multi-level underground parking. Further, a3D indexing also suits a case where multiple tunnels reside in closevicinity and are controlled centrally by a single CMS. In the lattercase, one of the entries to the three-elements index may serve as atunnel identification number.

FIG. 3 shows an example diagram 300 of an allocation of an orbitingsatellite from a list of satellites available for allocation, accordingto an embodiment. Here, a single satellite (e.g., a satellite 110) in anorbit 310 in a counterclockwise direction around earth with fiveindications of its positions 311-319 along this orbit 310 is shown. Theground position 320 of the tunnel 130 is indicated by a dark triangle,where a dashed line 330 indicates the horizon with respect to thetunnels' position 330. Two additional lines 342, 344 indicate margins(e.g. spare regions for compliance with regulation purposes) one for therising direction 342 and the other for the setting direction 344.Satellites' position 311 indicates a satellite approaching to a rise upposition.

This state triggers a checkup to verify if one of the pseudolites isallocated with this satellite parameters. If this is the case, thischeckup invokes a pseudolite allocation switching mechanism managed bythe CMS 150. As long as the satellite is visible (at positions 313-317)(i.e., where position 315 is the highest point at visible sky withrespect to the scene) an ID number identifying this satellite is omittedout of an available satellites list 350. The list 350 may be organizedin many forms. The underlined design for this list 350 is that it iseasy to pull out satellite ID for use at any time instance the systemrequires so.

In the tunnel 130, the satellites allocation may be used along theunderground space cyclically in a reusable fashion. Furthermore, goingdeeper in the tunnel 130, the system may use the satellites 110-114 inview as long as the transmitted signals of pseudolites 141-147 with thesame satellite ID do not interfere with each other. In this later casethe scheduler 262 can apply a fixed allocation method due to theinherent decoupling from the inner tunnel to the out-of-tunnel space.

According to an embodiment, the list 350 is maintained by placing thesatellite crossing the setting direction 344, at position 319 at the top352 of the list 350, as it is expected to have this satellite in a usestate for the longest time, and therefore has the most time ofavailability. Satellite which is allocated to a certain pseudolite andapproaches the rising time 342 at position 311 will be placed at thebottom of the list 354. In another embodiment, the list 350 is organizedperiodically by ordering all non-visible satellites by their ‘dark time’period in a descending order (i.e. by ‘dark time’ it is defined as thetime point of a satellite not being visible including the time marginsbefore it rises at position 311, and after it sets at position 319). Thesatellite with the longest time of usability will be placed in the topside of the table 352, while the satellite with least time of usabilitywill be placed in the bottom of the table 354. This placing and movingof the satellite ID within the list 350 may occur periodically (e.g.every 15 mins) or triggered by demand.

Once a satellite allocation request appears, the top ranked satellite‘352’ is pulled out for allocation 360, the occurrence of which may alsobe used to trigger another refresh of the list 350. At the same time, asthe satellite approaches the rising position 311 and becomes the leastavailable, the satellite is placed back 362 from being allocated on thebottom of the list 354.

It is further noted that the list 350 is not the only option forimplementing this function. In an embodiment, a software routine may besuggested by having all the involved parameters in the setting (e.g.,all satellites that are usable, their position in [x, y, z] or [azimuth,elevation], time-of-day, etc.) to derive the best usable satellite(i.e., usable for the longest time) for allocation. Anotherimplementation can use calculation of the schedule in advance for asubstantial period (e.g. day, week, month etc.) and use it as a staticinformation table.

FIG. 4 shows an example diagram 400 of a top-down view of a tunnel,according to an embodiment. The tunnel 130 is mounted with pseudolites141, 143, 145, 147 on the left side wall with respect to the vehicleheading, and pseudolites 140, 142, 144, 146 to the right-side wall withrespect to the vehicle heading. GNSS satellites 110, 112, 114 flyoverhead the tunnel 130. Here, the pseudolites 140-147 may be installedin a distributed fashion, where the baseband elements are placedremotely in a server room and the RF frontends are mounted on the wallsor as a full unit mounted remotely controlled.

As for the exact positioning of the pseudolites' antennas, in oneembodiment, the antennas' exact positioning is measured manually. Inanother embodiment, the determined location of the pseudolites' antennasare mounted in predefined spaces/distances. In this case, the locationof the pseudolites antennas are derived with reference to a singlepseudolite antenna position (e.g. at the entry 132 of the tunnel 130) isobtained using the predefined distance parameters. In anotherembodiment, the positions of the antennas are derived autonomously byapplying range measurements between the pseudolites antennas. The arrows410, 412, 414 indicate the ranges between pseudolites 140,141;pseudolites 141, 143; and pseudolites 140, 143, respectively. The rangemeasurements can be carried out using additional GNSS receivers (notshown) integrated with pseudolite station 420 ₁-420 _(n) (hereinafterpseudolite stations 420 or pseudolite station 420).

In another embodiment, a dedicated ranging RF based transceiver can beintegrated with a pseudolite such as UWB, Wi-Fi and other. In this case,the range measurements can be performed using several techniques such astime-of-arrival (ToA), time-difference-of-arrival (TDoA), time-of-flight(ToF), etc. To derive each of the pseudolite-stations 420 mounted on thetunnel wall location autonomously, at least three known positions ofpseudolites in a close vicinity to the pseudolite station 420 arerequired. Given the positions of this close vicinity, minimal set ofpseudolites and measuring the range of these pseudolites with to thoseof the other pseudolites with unknown location, the locations of theunknown pseudolites may be determined (i.e. in transmit and receivedistance). For example, a sequential positioning process using anautonomous pseudolite positioning scheme may be applied, where theprocess starts with three pseudolites with known fixed locations (e.g.the first pseudolites may be in close vicinity and out of the tunnel130).

Alternatively, dedicated devices designed to acquire the pseudolites'positions (e.g., based on traditional GNSS precise positioningtechnique) are positioned temporarily outside of the tunnel. In thisembodiment, the pseudolite with an unknown location measures the rangeto the three (or more) first pseudolites with a known locationpseudolites to derive its own location. The process can be based on atleast three known location pseudolites (that will play the role ofanchors), and it is assumed that the pseudolites 140-142 are located atthe area. This way, the anchors (i.e., the pseudolites with the knownfixed locations) can derive their locations based on the operationalGNSS satellites 140-142. Once the anchors' locations are derived andfixed, a next pseudolite station 420 residing, for example, one stagedeeper into the tunnel starts to perform ranging measurements, accordingto FIG. 4, to all the pseudolites with known locations (i.e., anchors).This process sequentially progresses stage by stage into the tunnel andcontinues until it acquires all the tunnels' pseudolites locations.

FIG. 5 is an example flowchart 500 illustrating a method for providingnavigation underground, according to an embodiment. The method 500 maybe performed by the CMS 150.

At S510, ephemeris data of a plurality of satellites in orbit isreceived. Next, at S520, a schedule of the plurality of satellites inorbit is determined based on the received ephemeris data. At S530, alocation of each pseudolite within an underground space is obtained.Then, at S540, a plurality of satellites parameters to configure thepseudolites based on their obtained locations of the satellites'schedule is determined. Here, the plurality of satellites parameters mayinclude one of a physical signal modulation parameter or a broadcastdata parameter.

Next, at S550, each pseudolites is configured with the plurality of thepseudolites parameters determined for the respective pseudolite. Then,at S560, each pseudolite is controlled to broadcast a signal based onthe configured satellites parameters. The signals broadcasted by thepseudolites simulate the GNSS signals as would have been transmitted bythe satellites in orbit.

The various embodiments disclosed herein can be implemented as hardware,firmware, software, or any combination thereof. Moreover, the softwareis preferably implemented as an application program tangibly embodied ona program storage unit or computer readable medium consisting of parts,or of certain devices and/or a combination of devices. The applicationprogram may be uploaded to, and executed by, a machine comprising anysuitable architecture. Preferably, the machine is implemented on acomputer platform having hardware such as one or more central processingunits (“CPUs”), a memory, and input/output interfaces. The computerplatform may also include an operating system and microinstruction code.The various processes and functions described herein may be either partof the microinstruction code or part of the application program, or anycombination thereof, which may be executed by a CPU, whether or not sucha computer or processor is explicitly shown. In addition, various otherperipheral units may be connected to the computer platform such as anadditional data storage unit and a printing unit. Furthermore, anon-transitory computer readable medium is any computer readable mediumexcept for a transitory propagating signal.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the principlesof the disclosed embodiment and the concepts contributed by the inventorto furthering the art, and are to be construed as being withoutlimitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosed embodiments, as well as specific examplesthereof, are intended to encompass both structural and functionalequivalents thereof. Additionally, it is intended that such equivalentsinclude both currently known equivalents as well as equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations are generally used herein as a convenient method ofdistinguishing between two or more elements or instances of an element.Thus, a reference to first and second elements does not mean that onlytwo elements may be employed there or that the first element mustprecede the second element in some manner. Also, unless statedotherwise, a set of elements comprises one or more elements.

As used herein, the phrase “at least one of” followed by a listing ofitems means that any of the listed items can be utilized individually,or any combination of two or more of the listed items can be utilized.For example, if a system is described as including “at least one of A,B, and C,” the system can include A alone; B alone; C alone; 2A; 2B; 2C;3A; A and B in combination; B and C in combination; A and C incombination; A, B, and C in combination; 2A and C in combination; A, 3B,and 2C in combination; and the like.

What is claimed is:
 1. A method for providing navigation through anunderground space, comprising: receiving ephemeris data of a pluralityof satellites in orbit at a location of the underground space;determining a schedule of the plurality of satellites in orbit;obtaining location of a plurality of pseudolites within the undergroundspace; determining satellite parameters to configure each of theplurality of pseudolites, wherein the satellite parameters aredetermined based on the obtained location of each pseudolite and thedetermined satellite schedule, and wherein the satellite parametersinclude at least a signal modulation parameter and a broadcast dataparameter; configuring each of the plurality of pseudolites with therespective satellite parameters; and controlling the plurality ofpseudolites to broadcast satellite signals based on the determinedsatellite parameters, wherein the broadcasted satellite signals simulatelocations of the plurality of satellites in orbit.
 2. The method ofclaim 1, wherein further comprising: determining the locations of theplurality of pseudolites based on relative range measurement.
 3. Themethod of claim 2, further comprising: determining a location of a firstset of plurality of pseudolites based on an allocation of at least oneof the first set of plurality of pseudolites with the plurality ofsatellites; determining a range from the first set of plurality ofpseudolites to a second set of plurality of pseudolites; and determininglocation of additional plurality of pseudolites, based on the determinedlocation of the at least three plurality of pseudolites.
 4. The methodof claim 1, wherein the schedule of the plurality of satellites in orbitincludes a list of a plurality of satellite IDs, each of the pluralityof satellite IDs corresponding to one of the plurality of satellites inthe orbit.
 5. The method of claim 4, further comprising: allocating eachof the plurality of pseudolites with the list of the plurality ofsatellite IDs corresponding with a plurality of non-visible satellite,based on the schedule, upon the movement of the satellite out of thevisible position; updating the schedule of the plurality of satellitesin orbit, upon a movement of the plurality of satellites into or out ofa visible position for allocation with the pseudolite; and providing theupdated schedule.
 6. The method of claim 4, wherein the schedule isordered by an amount of time a satellite is available for allocationwith the pseudolite.
 7. The method of claim 4, wherein: the satellite IDcorresponding with a satellite that has a longest time of usability forallocation with the pseudolite, and is in a setting position is placedat a highest priority of the schedule for allocation; and the satelliteID corresponding with a satellite that has a shortest time of usabilityfor allocation with the pseudolite, and is in a rising position isplaced at a least priority of the list for allocation.
 8. The method ofclaim 1, wherein each of the plurality of pseudolites is configured withsamples vector derived based on the determined satellite parameters. 9.The method of claim 1, wherein the broadcasted satellites signal by arecompliant with other signals broadcasted by the plurality of satellitesin orbit.
 10. A non-transitory computer readable medium having storedthereon instructions for causing a processing circuitry to execute aprocess, the process comprising: receiving ephemeris data of a pluralityof satellites in orbit at a location of the underground space;determining a schedule of the plurality of satellites in orbit;obtaining location of a plurality of pseudolites within the undergroundspace; determining satellite parameters to configure each of theplurality of pseudolites, wherein the satellite parameters aredetermined based on the obtained location of each pseudolites and thedetermined satellite schedule, and wherein the satellite parametersinclude at least a signal modulation parameter and a broadcast dataparameter; configuring each of the plurality of pseudolites with therespective satellite parameters; and controlling the plurality ofpseudolites to broadcast satellite signals based on the determinedsatellite parameters, wherein the broadcasted satellite signals simulatelocations of the plurality of satellites in orbit.
 11. A system formobile underground navigation using GNSS receiver, comprising: aplurality of pseudolites; a processing circuitry; and a memory, thememory containing instructions that, when executed by the processingcircuitry, configure the system to: receive ephemeris data of aplurality of satellites in orbit at a location of the underground space;determine a schedule of the plurality of satellites in orbit; obtainlocation of a plurality of pseudolites within the underground space;determine satellite parameters to configure each of the plurality ofpseudolites, wherein the satellite parameters are determined based onthe obtained location of each pseudolites and the determined satelliteschedule, and wherein the satellite parameters include at least a signalmodulation parameter and a broadcast data parameter; configure each ofthe plurality of pseudolites with the respective satellite parameters;and control the plurality of pseudolites to broadcast satellite signalsbased on the determined satellite parameters, wherein the broadcastedsatellite signals simulate locations of the plurality of satellites inorbit.
 12. The system of claim 11, wherein the system is furtherconfigured to determine the locations of the plurality of pseudolitesbased on relative range measurement.
 13. The system of claim 12, whereinthe system is further configured to: determine a location of a first setof plurality of pseudolites based on an allocation of at least one ofthe first set of plurality of pseudolites with the plurality ofsatellites; determine a range from the first set of plurality ofpseudolites to a second set of plurality of pseudolites; and determine alocation of additional plurality of pseudolites, based on the determinedlocation of the at least three plurality of pseudolites.
 14. The systemof claim 11, wherein the schedule of the of the plurality of satellitesin orbit includes a list of a plurality of satellite IDs, each of theplurality of satellite IDs corresponding to one of the plurality ofsatellites in the orbit.
 15. The system of claim 14, wherein the systemis further configured to: allocate each of the plurality of pseudoliteswith the list of the plurality of satellite IDs corresponding with aplurality of non-visible satellite, based on the schedule, upon themovement of the satellite out of the visible position; update theschedule of the plurality of satellites in orbit, upon a movement of theplurality of satellites into or out of a visible position for allocationwith the pseudolite; and provide the updated schedule.
 16. The system ofclaim 14, wherein the schedule is ordered by an amount of time asatellite is available for allocation with the pseudolite.
 17. Thesystem of claim 14, wherein: the satellite ID corresponding with asatellite that has a longest time of usability for allocation with thepseudolite, and is in a setting position is placed at a highest priorityof the schedule for allocation; and the satellite ID corresponding witha satellite that has a shortest time of usability for allocation withthe pseudolite, and is in a rising position is placed at a leastpriority of the list for allocation.
 18. The system of claim 14, whereineach of the plurality of pseudolites is configured with samples vectorderived based on the determined satellite parameters.
 19. The system ofclaim 11, wherein the broadcasted satellites signal by are compliantwith other signals broadcasted by the plurality of satellites in orbit.